## Solving Integral Equations (2) – Square Integrable Functions, Norms, Trial Method

Square Integrable function or quadratically integrable function $\mathfrak{L}_2$ function A function $y(x)$ is said to be square integrable or $\mathfrak{L}_2$ function on the interval $(a,b)$ if $$\displaystyle {\int_a^b} {|y(x)|}^2 dx <\infty$$ or $$\displaystyle {\int_a^b} y(x) \bar{y}(x) dx <\infty$$. For further reading, I suggest this Wikipedia page. $y(x)$ is then also called 'regular function'. The kernel $K(x,t)$ , a function of two variables is an $\mathfrak{L_2}$ - function if atleast one of the following is true: $\int_{x=a}^b \int_{t=a}^b |K(x,t)|^2 dx dt <\infty$ \$\int_{t=a}^b |K(x,t)|^2 dx…